The present invention relates to catalyst components for the polymerization of olefins CH2xe2x95x90CHR, wherein R is hydrogen or a hydrocarbon radical having 1-12 carbon atoms, the catalysts obtained therefrom and their use in the polymerization of said olefins.
Catalysts supported on magnesium dihalides in active form are well known in the literature. The first catalysts of this type are described in U.S. Pat. No. 4,298,718 and 4,495,338.
A further development to the supported catalysis has been given by the catalysts showing a controlled morphology, in particular having spherical shape. These catalysts are able to give polymers which, by duplicating the shape of the catalyst and showing good morphological properties, allow simplifications in the preparation and/or post treatment processes of polymers.
Examples of catalysts having controlled morphology are described in U.S. Pat. Nos. 3,953,414 and 4,399,054. In the latter patent the components are obtained starting from spherical adducts of MgCl2 with about 3 mols of alcohol. The preparation of the catalytic component can be carried out in different ways, for example by lowering the alcohol content of the adduct, by treatment under vacuum, up to 2.5-2 mols for each MgCl2 mole, then allowing the thus obtained support to react with TiCl4. Alternatively the adduct containing about 3 moles of alcohol is treated with AlEt3 and thereafter is reacted with TiCl4. In each case components having a nitrogen porosity between 0.3 and 0.4 cm3/g, a surface area between 300 and 500 m2/g and an average pore radius comprised between about 15 and 30 xc3x85 are obtained.
Catalysts prepared from TiCl4 and granular MgCl2 by spray-drying of an alcoholic magnesium chloride solution and subsequent supporting of the titanium compound are described in patent EP-B-65700 and EP-B-243327. However, the polymer obtained with these catalysts does not show morphological characteristics of interest. In particular, the bulk density is not sufficiently high. Furthermore, the activity of the catalyst is rather low.
A method for increasing the activity of these catalysts is described in patent EP-A-281524. The catalysts are prepared by supporting titanium alcoholates on a MgCl2-ethanol adduct, containing from 18 to 25% by weight of ethanol, made spherical by spray-drying of the ethanol solution and subsequent chemical treatment with Et2AlCl or Et3Al2Cl3. The conditions for the preparation of the support are critical and are reflected in the morphological stability of the polymer obtained. Polymers in form of heterogeneous powders are obtained, for example, using supports with an alcohol content not comprised within the critical range of 18-25or by using compounds different from Et2AlCl and Et3Al2Cl3. Furthermore, in order to have sufficiently high yields, the Ti content in the solid component is always higher than 8% by weight.
Catalysts obtained from MgCl2-alcohols adducts, wherein the adduct generally containing 3 mols of alcohol for each mole of MgCl2 is dealcoholated by thermal treatment up to alcohol levels generally comprised between 0.2 and 2 mols and thereafter is reacted with an excess of titanium tetrachloride optionally containing a dissolved electron-donor compound, are known from the patent application EP-A-395083.
These catalysts are able to give polymers in the form of spheroidal particles with good morphological properties, in particular high bulk density.
The solid components of the catalysts described in EP-A-395083 are characterized by high surface areas and microporosity (more than 50% of the pore radius are higher than 100 xc3x85, but lower than 800 xc3x85).
Spherical catalyst components are now unexpectedly found for the polymerization of olefins having low values of surface area (measured by the BET method) and at the same time having high values of total porosity (measured by the mercurium method, hereinafter described) and distribution of the pore radius shifted towards values higher than 800 xc3x85.
The components of the invention are able to give catalysts characterized by a high activity in the polymerization processes of olefins CH2xe2x95x90CHR, wherein R is hydrogen or a hydrocarbon radical having 1-12 carbon atoms, and able to give polymers endowed with valuable morphological properties, in particular having high bulk density values notwithstanding the remarkable macroporosity of the solid components forming the catalyst. Therefore, they are particularly suited to the modern vapour phase polymerization processes of the olefins wherein the high productivity of catalysts must be accompanied by the morphological stability of the same.
The spherical components of the invention comprise a titanium compound, supported on a magnesium halide, containing more than one Ti-halogen bond and optionally containing groups different from halogen in amounts lower than 0.5 mole for each mole of titanium and are characterized by having a surface area, measured by the BET method, of lower than 70 m2/g, a total porosity, measured by the merctrium method, of higher than 0.5 cm3/g and a pore radius such that at least 50% have values higher than 800 xc3x85.
The total porosity is generally comprised between 0.6 and 1.2 cm3/g and the area is preferably comprised between 30 and 70 m2/g. The porosity measured by the BET method is generally lower than 0.25 cm3/g.
Spherical components of particular interest are further-more characterized by the fact that at least 80% of pores have a radius up to 15,000 xc3x85 and porosity comprised between 0.6 and 0.9 cm3/g.
The particles of solid component have substantially spherical morphology and average diameter comprised between 5 and 150 xcexcm. As particles having substantially spherical morphology, those are meant wherein the ratio between the greater axis and the smaller axis is equal to or lower than 1.5 and preferably lower than 1.3.
Magnesium dihalides comprised in the spherical component of the invention are in the active form and are characterized by X-ray spectra in which the most intense diffraction line which appears in the spectrum of the non active halide is diminished in intensity and is substituted by a halo of which the maximum of intensity is shifted towards angles lower than those of the most intense line.
Preferably, the magnesium dihalide is MgCl2.
The components of the invention-can also comprise an electron compound (internal donor), selected for example among ethers, esters, amines and ketones. Said compound is necessary when the component is used in the stereoregular (co)polymerization of olefins such as propylene, 1-butene, 4-methyl-pentene-1; the internal donor can be advantageously used also when wanting to prepare linear low density polyethylenes (LLD-PE) having a narrow molecular weight distribution.
In particular, the internal electron donor compound can be selected from the alkyl, cycloalkyl and aryl ether and esters of polycarboxylic acids, such as for example esters of phthalic and maleic acid, in particular n-butylphthalate, di-isobutylphthalate, di-n-octylphthalate.
Other electron donor compound advantageously used are the 1,3-diethers of the formula: 
wherein RI, RII, the same or different from each other, are alkyl, cycloalkyl, aryl radicals having 1-18 carbon atoms and RIII, RIV, the same or different from each other, are alkyl radicals having 1-4 carbon atoms.
The electron donor compound is generally present in molar ratio with respect to the magnesium comprised between 1:4 and 1:20.
The preferred titanium compounds have the formula Ti(OR)nXyxe2x88x92n, wherein n is a number comprised between 0 and 0.5 inclusive, y is the valency of titanium, R is an alkyl, cycloalkyl or aryl radical having 2-8 carbon atoms or a COR group, X is halogen. In particular R can be n-butyl, isobutyl, 2-ethylhexyl, n-octyl and phenyl; X is preferably chlorine.
If y is 4, n varies preferably from 0 to 0.02; if y is 3, n varies preferably from 0 to 0.015.
Components of the invention form catalysts, for the polymerization of alpha-olefins CH2xe2x95x90CHR wherein R is hydrogen or a hydrocarbon radical having 1-12 carbon atoms by reaction with Al-alkyl compounds. In particular Al-trialkyl compounds, for example Al-trimethyl, Al-triethyl , Al-tri-n-butyl, Al-triisobutyl are preferred. The Al/Ti ratio is higher than 1 and is generally comprised between 20 and 800.
In the case of the stereoregular polymerization of xcex1-olefins such as for example propylene and 1-butene, an electron donor compound (external donor) which can be the same or different from the compound used as internal donor is also generally used in the preparation of the catalyst.
In the case in which the internal donor is an ester of a polycarboxylic acid, in particular a phthalate, the external donor is preferably selected from the silane compounds containing at least a Si-OR link, having the formula RI4xe2x88x92nSi(ORIII)n, wherein RI is an alkyl, cycloalkyl, aryl radical having 1-18 carbon atoms, RIII is an alkyl radical having 1-4 carbon atoms and n is a number comprised between 1 and 3. Examples of these silanes are methyl-cyclohexyl-dimethoxysilane, diphenyl-dimet-hoxysilane, methyl-t-butyl-dimethoxysilane.
It is possible to advantageously use also the 1,3 diethers having the previously described formula. In the case in which the internal donor is one of these diethers, the use of an external donor can be avoided, as the stereospecificity of the catalyst is already sufficiently high.
A method suitable for the preparation of spherical components of the invention comprises the reaction between:
(a) a compound MgCl2.mROH, wherein 0xe2x89xa6mxe2x89xa60.5 and R is an alkyl, cycloalkyl or aryl radical having 1-12 carbon atoms;
(b) a titanium compound of the formula Ti(OR)nXyxe2x88x92n, in which n is comprised between 0 and 0,5, y is the valency of titanium, X is halogen and R is an alkyl radical having 2-8 carbon atoms or a COR group.
The compound (a) is prepared by chemical dealcoholation of adducts MgCl2.pROH, with 0.1xe2x89xa6pxe2x89xa62, in turn obtained by thermal dealcoholation of adducts MgCl2.qROH, wherein 2.5xe2x89xa6qxe2x89xa63.5. In the reaction between the compound (b) and the compound (a) the molar ratio Ti/Mg is stoichiometric or higher; preferably this ratio in higher than 3. The Ti/Mg molar ratio may also be from 0.05 to 3.
The process can also comprise the use of an electron donor compound (internal donor) of the previously described type in the reaction step between the compound (a) and the titanium compound (b). Molar ratios between internal donor and magnesium halide are generally comprised between 1:2 and 1:20.
Adducts MgCl2.qROH are prepared in spherical form from molten adducts by emulsifying them in liquid hydrocarbon and thereafter solidifying them by quick cooling. Representative methods for the preparation of these spheralized adducts are reported in U.S. Pat. No. 4,469,648, whose description is herein included as reference. Another useable method for the spheralization is spray cooling described in U.S. Pat. No. 5,100,849 and 4,829,034 whose description is herein included as reference. Spheralized adducts thus obtained are subjected to thermal dealcoholation at temperatures comprised between 50 and 150xc2x0 C. until the alcohol content is reduced to values lower than 2 and preferably comprised between 1.5 and 0.3 moles per mole of magnesium dihalide and finally treated with chemical reagents able to react with OH groups of the alcohol and further dealcoholate the adduct until the content is reduced to values comprised between 0 and 0.5 moles per mole of Mg, preferably lower than 0.3 moles.
The treatment with chemical dealcoholating agents is carried out using sufficient amounts of agent to react with the OH present in the alcohol of the adduct. It is preferable to work with a slight excess of said agent which is then separated before reacting the titanium compound with the so obtained support.
The chemical dealcoholating agents comprise for example Al-alkyl compounds, such as for example Al(C2H5)3, Al(C2H5)2Cl, Al(iBu)3, halogenated Si and Sn compounds such as SiCl4 and SnCl4.
Preferred titanium compounds (b) are titanium tetrahalides, in particular TiCl4. In this case the compound obtained after chemical dealcoholation is suspended at low temperature, in an excess of TiCl4. The suspension is then heated at temperatures comprised between 80 and 135xc2x0 C. and is kept this temperature for a time period comprised between 0.5 and 2 hours. The excess titanium is separated at high temperatures by filtration or sedimentation and siphoning, also carried out at high temperatures. The treatment with TiCl4 can optionally be repeated many times. The treatment with TiCl4 may also be carried out in hydrocarbon solution.
In the case in which the catalytic component must comprise an internal electron donor of the previously described type, this can be advantageously added during the treatment with TiCl4, using the previously described molar ratios with respect to the magnesium.
If the titanium compound is a solid, such as for example TiCl3, this can be supported on the magnesium halide by dissolving it in the starting molten adduct.
If the chemical dealcoholation of the adduct MgCl2.pROH is carried out with agents having the capacity to reduce, for example an Al-alkyl compound such as Al-triethyl, the so obtained compound, before the reaction with the titanium compound, can be treated with a deactivating agent, for example O2 or an alcohol, in order to deactivate the Al-triethyl optionally still present thus avoiding the reduction of the titanium compound.
The treatment with deactivating agents is avoided when it is desired to at least partially reduce the titanium compound. If, on the contrary, a higher degree of reduction of the titanium compound is desired, the process for the preparation of the component can advantageously comprise the use of reducing agents.
As examples of reducing compounds, Al-alkyls and the Al-alkyl halides or the silicon compounds, such as polyhydrosiloxanes, can be mentioned.
As previously indicated the spherical components of the invention and catalysts obtained therefrom find applications in the processes for the preparation of several types of olefinic polymers.
For examples the following can be prepared: high density ethylene polymers (HDPE, having a density higher than 0.940 g/cc), comprising ethylene homopolymers and copolymers of ethylene with alpha-olefins having 3-12 carbon atoms; linear low density polyethylenes (LLDPE, having a density lower than 0.940 g/cc) and very low density and-ultra low density (VLDPE and ULDPE, having a density lower than 0.920 g/cc, to 0.880 g/cc) consisting of copolymers of ethylene with one or more alpha-olefins having from 3 to 12 carbon atoms, having a mole content of units derived from the ethylene higher than 80%; elastomeric copolymers of ethylene and propylene and elastomeric terpolymers of ethylene and propylene with smaller proportions of a diene having a content by weight of units derived from the ethylene comprised between about 30 and 70%, isotactic polypropylenes and crystalline copolymers of propylene and ethylene and/or other alpha-olefins having a content of units derived from propylene higher than 85% by weight; shock resistant polymers of propylene obtained by sequential polymerization of propylene and mixtures of propylene with ethylene, containing up to 30% by weight of ethylene; copolymers of propylene and 1-butene having a number of units derived from 1-butene comprised between 10 and 40% by weight.
The polymerization of olefins in the presence of catalysts obtained from the catalytic components of the invention can be carried out according to known techniques either in liquid or gas phase using for example the known technique of the fluidized bed or under conditions wherein the polymer is mechanically stirred.
Examples of processes wherein it is possible to use the spherical components of the invention are described in Italian patent applications MI-91-A-000379 and MI-92-A-000589. In this process a precontacting step of the catalyst components, a prepolymerization step and a gas phase polymerization step in one or more reactors in a series of fluidized or mechanically stirred bed are comprised.
The following examples are given to illustrate and not to limit the invention itself.
The properties indicated are determined according to the following methods:
Porosity and surface area with nitrogen: are determined according to the B.E.T. method (apparatus used SORPTOMATIC 1900 by Carlo Erba).
Porosity and surface area with mercury: are determined by immersing a known amount of mercury into the dilatometer and then hydraulically increasing the mercury pressure in a gradual manner to 2000 kg/cm2. The pressure of introduction of the mercury into the pores depends on the diameters of the pores themselves. The measure is carried out using a porosimeter xe2x80x9cPorosimeter 2000 seriesxe2x80x9d by Carlo Erba. The porosity, the distribution of pores and the surface area is calculated from the data of the volume reduction of the mercury and applied pressure values.
Size of the catalyst particles: are determined according to a method based on the principle of the optical diffraction of the laser monochromatic light by means of the apparatus xe2x80x9cMalvern Instr. 2600xe2x80x9d.
MIE flow index: ASTM-D 1238
MIF flow index: ASTM-D 1238
Flowability: is the time employed for 100 g of polymer to flow through a funnel having an outlet hole of 1.25 cm diameter and the walls having a 20xc2x0 inclination to the vertical.
Bulk density: DIN-53194
Morphology and granulometric distribution of the polymer particles: ASTM-D 1921-63
Fraction soluble in xylene: determined at 25xc2x0 C.
Comonomer content: percentage by weight of comonomer determined by I.R. spectrum.
Effective density: ASTM-D 792